1. Field of the Invention
This invention relates to aqueous sodium silicate extended polyurethane foam systems.
2. Description of the Prior Art
Polyurethane foam technology is a highly developed art. Sales of polyurethane foam in 1970 exceeded 1 billion pounds in the United States. In general polyurethane foam is produced by combining the following ingredients:
1. A polyisocyanate;
2. A polyol;
3. A blowing agent, normally a halogenated hydrocarbon;
4. A suitable catalyst for the reaction of --OH and --N.dbd.C.dbd.O groups;
5. A surfactant to control cell size and distribution.
Customarily a sufficient amount of polyisocyanate is provided to combine with the --OH groups of the polyol. The polyurethane foam has densities of about 2 pounds per cubic foot to about 40 pounds per cubic foot. The material has excellent thermal insulating properties. Polyurethane foam is available in both rigid and flexible forms.
In addition to the foregoing materials other additives may be employed such as:
1. Particulate fillers;
2. Fibrous fillers;
3. Pigments and dyes;
4. Fire retardant additives which may be coreactive and which may constitute a part of the polyol ingredient;
5. Water.
Polyurethane foams are employed as flotation elements for aquatic vessels, as thermal insulation for heat transfer barriers, as spacer members, as fillers and encapsulating materials for sealing cavities, as wall and ceiling coverings, and as packaging materials, and other uses.
U.S. Pat. No. 3,607,794 (issued Sept. 21, 1971) concerns the production of silicate foams by reacting an aqueous sodium silicate with a polyisocyanate in the absence of a preformed resin.
French patent application No. 1,419,552, filed Oct. 23, 1958, describes insulation materials which include aqueous sodium silicate, polyisocyanate derivatives and resins.
U.S. Pat. No. 3,634,342 (issued Jan. 11, 1972) is directed to the addition of small quantities of aqueous sodium silicate to polyurethane foam to permit the foam to be depotted when that is desired. The amount of alkali metal silicate for this purpose is from 0.5 to 5.0%. The reference indicates that the action was too rapid to control when the amount of sodium silicate exceeded 5.0%.
Conventional polyurethane foam products are inflammable and their use in building products is discouraged. By employing selected polyester resins as the starting polyol ingredient, it is possible to produce a polyurethane foam which has a low flame spread rating (less than 25) in the STEINER tunnel test, ASTM E-84. See U.S. Pat. No. 3,676,376. The preparation and use of such acceptable flame retardant polyurethane foams is expensive because of the cost of the polyester resin.